1. Field of the Invention
The present invention relates generally to rotary fans with elongated blades configured to move large volumes of air at low rotational speeds. This type of fan is usually configured to be mounted with the blades in a horizontal plane and above the area where most of the air moving is to occur, and is generally referred to as a high volume low speed (HVLS) fan.
2. Description of the Prior Art
A high volume low speed fan will generally have at least 6 blades, in the majority of cases each blade being at least 4 feet in length. A primary use for HVLS fans is to move air for ventilation, temperature control and cooling of people and livestock in large, relatively open buildings without causing strong air currents that may disrupt work and stir up dust. An example of an HVLS fan is taught by U.S. Pat. No. 6,244,821 entitled LOW SPEED COOLING FAN. This fan uses blades with an airfoil cross-section to produce a slowly downwards-moving column of air with a minimal lateral component. The blades are formed from an aluminum extrusion with an added tapered flap fastened to the extrusion to improve the airflow characteristics.
U.S. Pat. No. 6,589,016 also entitled LOW SPEED COOLING FAN is a continuation of the '821 patent and teaches a further permutation of fan blade shape and length.
U.S. Pat. No. 6,817,835 also entitled LOW SPEED COOLING FAN is a continuation of the '016 patent, covering essentially the same invention as the '016 patent.
U.S. Pat. No. 6,939,108 entitled COOLING FAN WITH REINFORCED BLADE teaches a further version of the HVLS fan blades described in the '821, '016 and '835 patents, in particular providing the innovation of a reinforcing flange whose purposes are disclosed to be increased structural rigidity, increased downward thrust during rotation and overcoming some of the manufacturing difficulties inherent in the production of long extruded metal fan blades with a trailing edge.
The HVLS fans taught by the '821, '016, '835 and '108 patents all share several characteristics, having extruded aluminum blades with an airfoil cross-section optimized for a single direction of airflow and producing an airflow consistently described as columnar or cylindrical, with intentionally minimized lateral airflow components and an airspeed limited to the range of 3-5 mph. Further, the fans are consistently taught as being configured to be mounted to the roof or ceiling of the building where they are to be used. Additionally, the '821 and '016 patents teach a constant mounting angle of 8 degrees for the blades in order to achieve optimal airflow at air speeds in the range of 3 to 5 mph. The '821, '016, '835 and '108 patents also teach the use of the HVLS fans for circulating air in industrial buildings, cooling industrial buildings, and cooling individuals in industrial buildings.
There are several disadvantages to the fans taught by the '821, '016, '835 and '108 patents. Extruded fan blades are inherently limited in contour variation along their length by the nature of the manufacturing process and may require considerable and expensive post-processing to have any contour variation. Additionally, the fan blades taught by the '821, '016, '835 and '108 patents all require a separate end cap component, requiring yet more manufacturing and fastening operations. These fan blades are also highly optimized for a single direction of airflow and would not be capable of efficiently producing an upwards airflow, which is very limiting. The blades are also optimized for a particular limited range of mounting angles and for a columnar or cylindrical airflow profile, further limiting the utility of the inventions disclosed therein. In addition, the uses taught by the '821, '016, '835 and '108 patents do not include de-stacking of air thermal layers or general temperature control.
The '821, '016, '835 and '108 patents all teach mounting of the HVLS fan to a ceiling or roof, which limits the general use of the fan and specifically limits some aspects of the airflow by proximity to a surface. This mounting style and the teaching of an airspeed constrained to 3-5 mph even further limit the utility of these inventions.
When a fan starts up, there is a spike in energy use partially caused by air resistance against the blades. The steeper the blade angle, the greater the air resistance and resulting instantaneous energy demand. This spike also can cause long-term damage to the motor itself as well as to the control and drive circuitry. A better approach is to have a fan capable of varying the blade angle to allow startup with a zero or very small angle, and increasing the blade angle automatically once the fan is rotating. Additionally, having the capability to widely vary the blade angle and rotational speed allows for a much greater variety of airflow characteristics, thus permitting the fan to be optimized for a wider range of uses. This more flexible approach to fan use is further improved if the blade is shaped to allow equal but opposite air movement at positive and negative blade angles.
Bi-directional airflow also allows increased capability for the fan to perform de-stacking or destratifying of air layers for increased efficiency and energy savings in both cooling and heating. Having bi-directional airflow capability also allows multiple fans to be configured with mixed or alternating directions of airflow to further optimize the air movement within a building. Optimized air movement includes improved air mixing and heat destratification for more uniform air temperatures, thus enabling a building's heating and air conditioning systems to operate more efficiently.
The columnar or cylindrical airflow taught by the '821, '016, '835 and '108 patents also limits the utility of the HVLS fans. A distinctly conical airflow contour allows more uniform flow of air at the places in the building where people and livestock would actually be. Additionally, mounting HVLS fans to ceilings or roofs is not always desirable, as having the fans spaced more distantly from the ceiling or roof and closer to the middle of the building may allow far better airflow and efficiency of use. Further, a fan designed for more flexible mounting can be used in more locations, and to that end an additional HVLS fan improvement is to have a lower-profile fan body that fits in more locations.
A more capable HVLS fan has blades shaped to permit more versatile and uniform airflow, control to set variable blade angles including the ability to start the fan with approximately zero blade angle and then vary the blade angle continuously during fan use, efficient bi-directional airflow capability, a control unit allowing manual and programmed control over blade angle and rotational speed, and the ability for the fan to be installed at a height inside a variety of buildings where efficiency and degree of desired air movement would be maximized.
A key element of a more capable HVLS fan is the ability to efficiently vary blade angle over a range of at least +/−20 degrees. One way to achieve a variable blade angle is taught by U.S. Pat. No. 1,309,005 entitled ADJUSTABLE RADIATOR FAN which discloses an engine radiator cooling fan with a manually adjustable fan blade pitch angle. The '005 patent teaches a single direction of blade pitch adjustment and manual mechanical actuation of the pitch control via a hand lever, the adjustment mechanism including a sliding actuator shaft within a rotating tubular drive shaft, a disk slotted with an annular groove affixed on the sliding actuator shaft, and fan blades pivotally mounted to a hub with the mounting including crank pins rigidly connected to the blade pivots and engaging the annular groove in the disk. Similar inventions teaching fan or propeller blades pivoted by attached crank pins held within an annular groove on a disk or ring actuated within a rotating tubular drive shaft are taught by U.S. Pat. No. 1,491,589 entitled MOTOR FAN WHEEL, U.S. Pat. No. 2,152,983 entitled WATERCRAFT, U.S. Pat. No. 2,225,209 entitled MOTOR COOLING CONTROL, U.S. Pat. No. 2,478,244 entitled PITCH ADJUSTING MECHANISM FOR PROPELLERS, and U.S. Pat. No. 5,281,095 entitled VARIABLE-PITCH MECHANISM FOR A PROPELLER. The '005, '589, '983, '209, '244 and '095 patents all teach different versions of a generally similar actuation mechanism.
The '589 patent teaches a variable-pitch fan capable of dual directions of blade pitch adjustment that may be either manually or thermostatically actuated, with facility in the manually actuated version for reading the blade pitch angle from a calibrated dial plate located with the actuation control. The '983 patent teaches a manually actuated bell-crank style of mechanism to set the pitch angle of a propeller. The '209 patent teaches a thermostatically actuated mechanism for setting blade pitch angle, including a counteracting spring and only a single direction of pitch angle control. The '244 patent teaches a variable-pitch propeller capable of dual directions of blade pitch adjustment that is manually actuated with a detented hand-lever control, and incorporates a spring in the actuator mechanism to permit propeller blade feathering against excessive back-pressure. The '095 patent teaches a hydraulically actuated sliding grooved ring rather than a grooved disk for controlling blade pitch. In this configuration, the pitch angle control is external to the actual drive shaft, although inside of the housing retaining the propeller blades.